The invention relates to a method and an apparatus for the surface blasting, especially the ultrasonic shot peening, of gas turbine blades in the area of their blade roots.
Gas turbines, especially aircraft engines, have a rotor that is fitted with rotating rotor blades especially in the area of their compressor as well as their turbine, whereby the rotating rotor blades of the gas turbine are anchored via profiled blade roots in corresponding recesses of the gas turbine rotor. According to the state of the art, it is possible to profile the blade roots either according to the so-called fir tree design or according to the so-called dovetail design and to anchor the blade roots in correspondingly profiled recesses of the gas turbine rotor. The preferably fir tree profiled or dovetail profiled surfaces of a blade root of a gas turbine blade are also referred to as carrier or support surfaces.
During the operation of a gas turbine, the blade roots are strongly loaded or influenced especially by frictional wear on their profiled support surfaces. The wear rate in the area of the blade roots can be reduced in that the blade roots are hardened on their support surfaces by special surface treatment or processing methods. In this regard, preferably the shot peening is applied. In the conventional shot peening, a considerable surface roughening can arise on the support surfaces of the blade roots, whereby the fitting accuracy of the blade roots is negatively influenced or impaired.
In order to improve the treatment or processing quality arising during shot peening on blade roots of gas turbines that are to be processed, it is already known from the state of the art according to U.S. Pat. No. 6,536,109 B2, to harden the blade roots in the area of their profiled support surfaces by so-called ultrasonic shot peening. Thus, the U.S. Pat. No. 6,536,109 B2 discloses a corresponding apparatus with an ultrasonic sonotrode, whereby the ultrasonic sonotrode comprises a level or horizontally extending, vibrating or oscillating surface, and whereby a processing chamber extends above this oscillating surface. Gas turbine blades are arranged standing with their blade roots in the processing chamber for the processing thereof in the area of their support surfaces. In that regard, according to the U.S. Pat. No. 6,536,109 B2, the gas turbine blades to be processed are oriented standing in such a manner so that the profiled support surfaces of the blade roots that are to be processed extend essentially perpendicularly to the oscillating surface of the ultrasonic sonotrode. Herewith only an insufficient quality can be achieved in the shot peening of the profiled support surfaces of the blade roots.